A research group of University of Birmingham makes reference to 1-(2-fluoro-4-thio-beta-D-arabinofuranosyl)-5-methyluracil and 1-(2-fluoro-4-thio-beta-D-arabinofuranosyl)-5-iodocytosine in International Patent Application PCT/GB90/01518 (International Publication Number: WO 91/04982).
Further, a research group of NIH has recently made a report on such compounds as 1-(2,3-dideoxy-2-fluoro-4-thio-beta-D-erythro-pentafuranosyl)uracil represented by the following formula: ##STR2## provided that B is uracil in series a, and cytosine in series b (Tetrahedron Letters, 35, 7569-7572 (1994); Tetrahedron Letters, 35, 7573-7576 (1994); Chemistry Letters, 301-302 (1995)).
Thus, both of these groups have made reports on pyrimidine nucleosides, but are quite silent on purine nucleosides. An object of the present invention is therefore to provide novel and useful 9-(2-deoxy-2-fluoro-4-thio-beta-D-arabinofuranosyl)purine derivatives.